The present invention relates to a lubricating system, preferably for smaller refrigerating machinery of piston compressor type having a driven crankshaft with a substantially vertical extension.
Refrigerators and freezers use to a large extent compressors driven by a small electric motor and with a vertically extending driven crankshaft, normally having a rotary speed in the region of 2800-3400 revolutions/minute. The lubricating system for such compressors has for a long period of time been optimized for such a rotary speed, based on that a vertically extending crankshaft is made hollow, and with a lower conically reduced and downwardly open member, having the opening lowered into oil existing in the lower part of the compressor housing. When the crankshaft is rotating, the oil existing in the lower part of the conical member is thrown outwards/upwards by means of centrifugal force within the conical member. Since oil continuously is being supplied from below, the oil forced outwards/upwards within the conical member due to the rotation of the crankshaft will successively xe2x80x9cclimb upwardsxe2x80x9d within the hollow crankshaft, i.e. also on the cylindrical portion located above the conical means. The force whereby the oil is moved in direction upwards within the crankshaft is based on the conicity of the lower portion and by the rotary speed. However, the conicity is restricted by the outside dimensions given to the crankshaft, and crankshafts as used today have dimensions in the region of 20 mm. As a result, the lowest rotary speed (minimum number of revolutions) is approximately 1800 revolutions/minute.
A major disadvantage related to the above mentioned known lubricating systems is that the lubricating system has been optimized for a predetermined rotary speed, and that a reduction of rotary speed, intended to increase system efficiency, is not allowed. Practical tests have shown that a compressor having the above type of lubricating system and with a calculated length of service of 15 years at a rotary speed exceeding 2000 revolutions/minute receive a length of service reduced to only a few hours already when the rotary speed is reduced to 1500-1600 revolutions/minute.
The object of the present invention is to disclose a lubricating system facilitating totally acceptable lubrication at considerably lower rotary speed than what has previously been regarded as possible, and thereby meeting the demands of today related to increased system efficiency, i.e. a compressor cycle with reduced speed, which also may alternate with a compressor cycle having increased rotary speed. A compressor system according to the present invention also meets remaining requirements of such a lubricating system, namely that same should be accomplished at lowest possible cost, that it should include few components, and that it should have a design securing a long period of service. Continuous use of low rotary speed results in up to 20% increased system efficiency, something which obviously is most desirable.
The lubricating system according to the present invention is preferably intended for smaller refrigerating machinery of piston compressor type having a substantially vertically extending drive shaft, and it is mainly characterized in that a preferably substantially disc shaped member is arranged adjacent to the lower part of the drive shaft to be rotated by the rotary movement of the drive shaft and having a substantially in direction upwards extending peripheral edge portion, also including one or a number of oil transferring means for communication with oil in an underlying oil reservoir, said oil transferring means during a rotary movement being arranged to collect and transfer oil from the underlying oil reservoir to the upper plane of the preferably substantially disc shaped member, a tubular pipe being arranged having its lower open part directed in an opposed direction to the rotary direction of the preferably substantially disc shaped member adjacent to the peripheral part of same arranged to transfer oil as a Pitot pipe pump via the tubular pipe from the preferably substantially disc shaped member for lubrication of the piston compressor. The lower portion of the drive shaft may advantageously include a downwardly open conically reduced tubular member, extending down below the oil level in the underlying oil reservoir, at a high rotary speed being arranged with its internal surface, due to influence from centrifugal force, to collect and transfer oil through a channel taken up in the drive shaft for lubrication of the piston compressor, wherein pump action achieved by the conically reduced tubular member is arranged to lower the oil level in the underlying oil reservoir to a level at which the oil transferring means no longer take up contact with the oil in the underlying oil reservoir and/or that the oil transferring ability of said means is substantially completely reduced at high rotary speed.